Mechanical vibrations of a heart can produce heart sounds. Heart sounds occur with each cardiac cycle and can be classified according to the activity associated with the vibration. The first heart sound (S1) is the sound made during closure of the mitral and tricuspid valves. The second heart sound (S2) is made by the closure of the aortic and pulmonary valves. The third heart sound (S3) and fourth heart sound (S4) are often related to abnormal filling pressures of the left ventricle during diastole. Heart sounds can be useful indications of cardiac function status.
Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. The devices can be used to treat patients using electrical therapy or to aid a physician or caregiver in patient diagnosis through monitoring of a patient condition, or both. The devices can include or can be connected to electrodes in communication with circuitry to monitor electrical heart activity, or can include one or more sensors to monitor patient physiologic parameters.
Various systems and methods for sensing heart sounds using implantable medical devices have been proposed. For example, Stahmann et al., in U.S. Patent Application Publication No. 2008/0125820, titled “Adaptive Sampling of Heart Sounds,” refers to sensing heart sounds according to one or more parameters and altering the one or more parameters using a triggering event.